Fåhræus effect

Should not be confused with "Fåhræus–Lindqvist effect"

The dependence of apparent viscosity of human blood on the capillary size it is flowing through is identified as the Fåhræus–Lindqvist effect. There is a related but different effect called the Fåhræus effect.[1] This is the decrease in average concentration of red blood cells in human blood as the diameter of the glass tube in which it is flowing decreases. In other words, in blood vessels with diameters less than 500 micrometer, both the hematocrit decreases with decreasing capillary diameter. The Fåhræus effect definitely influences the Fåhræus–Lindqvist effect but the former is not the only cause of the later.[2]

Contents

Mathematical Model

Considering steady laminar fully developed blood flow in a small tube with radius of r_0, whole blood separates into a cell-free plasma layer along the tube wall and enriched central core. As a result, the tube hematocrit, H_t, is smaller than the out flow hematocrit, H_0. A simple mathematical treatment of the Fåhræus effect was shown in Sutera et al. (1970).[3] This seems to be the earliest analysis:

\frac{H_t}{ H_0 }=\frac{1}{2-(1-(\frac {\delta}{r_0}))^2}

where:

H_t is the tube hematocrit
H_0 is the outlet hematocrit
\delta is the cell-free plasma layer thickness
r_0 is the radius of the tube

Also, the following expression was developed by Pries et al (1990)[4] to represent tube hematocrit,H_t, as a function of discharge hematocrit,H_d, and tube diameter.

\frac{H_t}{ H_d }= H_d%2B(1%2BH_d)(1%2B1.7 exp (-0.415 D)-0.6exp(-0.011D))

where:

H_t is the tube hematocrit
H_d is the discharge hematocrit
D is the diameter of the tube

Further reading

See also

References

  1. ^ Fahraeus, R., (1929) The suspension stability of the blood. Physiol. Rev. 9, 241274.. 
  2. ^ Name(required). "Blood Flow and Fahraeus Effect". Nonoscience.info. http://www.nonoscience.info/2010/09/02/blood-flow-and-fahraeus-effect/. Retrieved 2011-05-09. 
  3. ^ Sutera, S. P., Seshadri, V., Croce, P. A. and Hochmuth, R. M. (1970). Capillary blood flow: II. Deformable model cells in tube flow Microvascular Research, 2 (4), 420-433 DOI: 10.1016/0026-2862(70)90035-X. 
  4. ^ Pries AR, Secomb TW, Gaehtgens P and Gross JF. Blood flow in microvascular networks: Experiments and simulation. Circulation Research 67:826-834, 1990.